The role of serpentinization and magmatism in the formation of decoupling interfaces at magma-poor rifted margins
Section snippets
Introduction and scientific context
Major progress has been made in understanding the architecture of magma-poor rifted margins (e.g., Peron-Pinvidic et al., 2013; Reston, 2009). At present, it is generally accepted that the transition zone located between the edge of continental and first unambiguous oceanic crusts, also referred to as the Ocean Continent Transition (OCT), can include a zone of exhumed subcontinental serpentinized mantle. The presence of such a basement type is attested at several distal rifted margins based on
Seismic observations: intra-basement reflections
In this section, we identify and characterize potential decoupling interfaces at Ocean Continent Transitions of magma-poor rifted margins. The studied areas are thus located between the edge of unambiguous continental and first oceanic crusts (Fig. 2). In this study we do neither investigate continental nor oceanic Mohos, nor the S-type reflections (localized landward of the continental crust termination) (Fig. 2). Except for the Iberia-Newfoundland rifted margins and the Tyrrhenian Sea where
Nature and origin of intra-mantle basement interfaces: constraints from geological observations and quantitative analyses
Our observations suggest that the UR and LR can be interpreted as distinct rooting levels for normal faults, and thus correspond to different decoupling interfaces (décollement levels). However, their nature and origin remain unclear from seismic observations only. Several hypotheses are possible to explain these décollements, such as (1) detachment/exhumation fault planes, (2) shear zones, (3) brittle-ductile transitions, (4) serpentinization fronts, (5) top of intrusive magmatic bodies (e.g.,
Serpentinization and accommodation of extensional deformation
Seismic and field studies show the presence of two major distinct decoupling levels in the basement of ultra-distal domains at magma-poor rifted margins. These decoupling levels are at different depths and appear to be associated with different processes. In the upper part of the lithosphere, extension is manifested by mantle exhumation along detachment faults. The serpentinization process occurring along these active exhumation faults leads to the formation of a major rheological interface at
Conclusions
Based on seismic observations, we highlighted the presence of two main intra-basement decoupling interfaces in the exhumed mantle domain at magma-poor rifted margins. Integrating physical properties of serpentinized rocks and constraints from Alpine field analogues allowed us to interpret and discuss the nature and origin of these interfaces. In particular, our results show the presence of a strong rheological interface at about 3 km below top basement. We suggest that this interface played a
Declaration of Competing Interest
None.
Acknowledgement
Seismic lines of the Antarctic surveys GA228 and GA229 were provided by Geoscience Australia after personal request and are published with the permission of Geoscience Australia. We also would like to thank I. Thinon and Ifremer for providing us the Norgasis 23 reflection seismic profile presented in this work. We kindly acknowledge Ekeabino Momoh for discussion and for the seismic image of the SWIR. This research was financed by Exxon Mobil as part of the CEIBA II project. We greatly thank
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Present address: Sorbonne Université, CNRS-INSU, Institut des Sciences de la Terre Paris, ISTeP UMR 7193, F-75005 Paris, France.